Recently, reductions in the size and weight of portable electronic equipment has led to the development of batteries for use in the portable electronic equipment. These batteries should have both high performance and large capacity characteristics. Furthermore, these batteries should be reliable and safe and be produced in a cost effective manner.
Batteries are generally classified as primary batteries (which can be used only once and are then disposed of) and secondary batteries (which can be recharged and used repeatedly). Primary batteries include manganese batteries, alkaline batteries, mercury batteries, and silver oxide batteries. Secondary batteries include lead-acid storage batteries, nickel-metal hydride (Ni-MH) batteries, sealed nickel-cadmium batteries, lithium metal batteries, lithium ion batteries, lithium polymer batteries, and lithium-sulfur batteries.
Lithium rechargeable batteries generate electric power using electrochemical reaction materials (“active materials”) for both the positive electrode and the negative electrode. Critical factors for determining battery performance (such as capacity, cycle-life, power, safety, and reliability) include the electrochemical characteristics and thermal stability of the active materials used. Thus, extensive research has been undertaken to improve these characteristics of positive and negative active materials.
Of the currently available active materials for the negative electrode, lithium metal has high electric capacity per unit mass and high electro negativity. Thus, lithium metal can be well adapted for use in high capacity and high voltage battery cells. However, since it is difficult to ensure the safety of a battery using lithium metal, other materials capable of reversibly deintercalating and intercalating lithium ions are being used as the negative active materials in rechargeable lithium batteries.
Lithium rechargeable batteries generate electrical energy from changes in chemical potential during intercalation/deintercalation of lithium ions at the positive and negative electrodes. Lithium rechargeable batteries use positive and negative active materials that reversibly intercalate or deintercalate lithium ions during charge and discharge reactions. The lithium rechargeable batteries also contain organic electrolytes or polymer electrolytes positioned between the positive and negative electrodes.
The electrolyte may include a cyclic carbonate having a high dielectric constant (such as propylene carbonate, ethylene propylene carbonate, and so on) and a linear carbonate having low viscosity (such as diethyl carbonate, methylethyl propylene carbonate, dimethyl carbonate, and so on). The electrolyte may include a mixed solvent including a cyclic carbonate and a linear carbonate.
However, such an electrolyte is easily decomposed on an electrically active electrode, and the decomposed product may increase internal resistance of the battery. Accordingly, charge and discharge characteristics of the battery deteriorate and cycle-life decreases.
The information disclosed in this Background section is provided for enhancing the understanding of the present invention and may contain information that is not prior art or that is already known to persons of ordinary skill in the art.